The present invention relates to printed circuit boards and in particular to a printed circuit board providing improved attachment of printed circuit board traces to individual wire conductors.
Printed circuit boards provide a generally planar insulating substrate supporting a pattern of conductive traces that can be used to interconnect electrical components of an electrical circuit. The traces may be rapidly fabricated, for example, by a photo etching processes. Separate conductive pads may be placed on the front and back surfaces of the printed circuit board to surround opposite sides of a hole passing through the printed circuit board. Further, these pads may be connected by a conductive material (via) extending through the hole between the pads by a “plate through” process allowing conductive traces to pass between sides of the printed circuit boards.
The electrical components may be attached to the traces in a number of ways. When the electrical components have wire leads (through hole devices), the printed circuit board may include holes through which the wire leads of the components may be inserted. The holes are typically surrounded by a pad of conductive material connected to the traces and the leads of the component may be soldered to the pad. Alternatively, traces may provide for pads to which leads or pads are attached without through holes but held simply by the mechanical joint provided by the solder. These devices are termed “surface mount devices”.
Components may be rapidly assembled to the printed circuit board by computerized “pick and place” devices or similar machines and soldered to the traces by wave soldering, reflow soldering ovens or the like. After soldering, the electrical components are electrically and mechanically secured in a robust physical assembly.
Often the printed circuit board must communicate with other electrical devices through a wiring harness of separate wire conductors each providing a multi strand or single-strand conductor surrounded by an insulating jacket. The same technique used to attach the through hole electrical components to the printed circuit board may be used to connect harness wires to the printed circuit board. That is, each of the wires may have a portion of the insulation at the connecting end of wire removed (stripped) to expose a length of conductor and the conductor may be inserted through a hole in the printed circuit board surrounded by a conductive pad which is soldered to the conductor.
Generally insertion of the conductors of wires through printed circuit board holes is performed manually and can be difficult because of the need to thread the conductors individually through the holes without dislodging previously inserted but unsoldered conductors. Inserting the conductors one wire at a time can require substantial bending of the individual conductors to accommodate their different stages of insertion. Multi-strand conductors can sometimes be unraveled during this insertion process to create inadvertent loose conductor strands that may cause undesirable electrical shorting. This latter problem can be reduced by tinning the exposed conductors (pre-coating them with solder) before installation in the printed circuit board, but this requires an additional step that may not be desired.